1. Field of the Invention.
This invention relates generally to apparatus and processes for water and wastewater treatment and, more particularly, to such apparatus and processes which employ intra-channel clarification.
2. Prior Art.
Various processes are employed to treat sewage, as well as water for drinking. Some employ very large and complex pieces of equipment, and are utilized in situations involving significant volumes of influent to be treated. Other processes are accomplished on a much smaller scale. Plants employing small scale treatment processes are often referred to as "package plants", due to the ability to package and ship an entire plant as a unit. In sewage treatment, such plants are used to treat a single residential subdivision or single commercial application without the necessity of transmitting sewage to a large central treatment site. The same is true in water treatment, where small water systems cannot justify large treatment operations.
A common package sewage treatment plant employes a circular tank containing aeration equipment. Influent sewage is aerated in the tank. In a settling chamber, aerated floc is allowed to settle out and is returned to the tank, usually by pumping. Clarified water is skimmed from the settling chamber and is removed from the tank by either gravity flow or pumping.
In a package water treatment plant, the process is similar. Untreated water is pumped into a circular tank where a flocculant is added, causing solid particules in the water to coalesce. The water is mixed to encourage full utilization of the flocculant. In a settling chamber, the floc is allowed to settle and clarified water is skimmed and removed.
The efficiency of package sewage treatment plants has been questioned, as has the energy consumption of such plants. With increasing effulent quality standards, a need has developed for a more efficient plant which will function adequately under peak loading conditions while consuming a minimum amount of energy. Grit removal is also a problem which must be addressed, since small scale plants accumulate grit (such as sand) just as do large scale plants.
Various types of aerobic treatment methods are employed in large scale sewage treatment plants. One method which has proven to be highly successful utilizes an oxidation ditch for sewage aeration, whereby a flow of aerated sewage is continuously circulated in a generally oval-shaped ditch. Clarification of the aerated sewage is accomplished in various ways. Some plants use external clarifiers, which are large tanks into which mixed liquor from the oxidation ditch is pumped. Sludge floc is allowed to settle and is pumped back into the ditch for further aeration. Clarified effluent is drawn off the top of the external clarifier. The external clarifier process is very similar to that used in the prior art package plants.
A relatively new technology has developed whereby clarification takes place within the oxidation ditch itself. This technology is known as "intra-channel clarification". Various types of intra-channel clarifiers are disclosed by way of example in the following U.S. patents:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 4,362,625 Beard 4,383,922 Beard 4,457,844 Beard ______________________________________
Applicant has utilized the principles of intra-channel clarification to develop a treatment system having the advantages of oxidation ditch efficiency and package plant utility. Applicant's invention is likewise useful for water treatment.